Model 1 — Predator—Prey Relationships Relationship …

EcologicalRelationships

What symbiotic relationships are seen in ecosystems?

Why?

All living organismsneed each other in some way to survive.This can include the interactions between predators and their prey, the close associations between and among living things (symbiosis), or the competitive relationships between and among species. All of these relationships may be equally advantageous to the parties involved,or they may be more beneficialto one organismover the other.

Model 1 --Predator--Prey Relationships

Relationship between Snowshoe Hares and Lynx

180

Number of hares

Number of lynx

160

140

120

100

80

60

40

20

1845 1850 1855 1860 1865 1870 1875 1880 1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935

Year

l. Refer to the graph in Model l. a. What does the y axis on che left represent? Number of hares. b. What does chey axison the right represent? Number oflynx. c. For both y axes,what value do che numbers on the axes need to be multiplied by? 103 or 1000.

2. What was cheapproximatepopulation of snowshoehares in 1865? 155,000.

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3. What was the approximate population of lynx in 1865? 5000.

4. When the number of snowshoehares is high, what happens to the number of lynx?Use actual data from the graph to support your observation. The number of lynx is usually also high (any data points acceptable).

5. What happens to the population of lynx as the number of snowshoehares decreases?Use actual data from the graph to support your observation. The population oflynx declines also (any data points acceptable).

6. Propose an explanationfor the apparent causeand effectrelationship between the populations of lynx and hares. Becausea lot offood is available (snowshoehare) more lynx are likely to survive and their population can Increase.

7. What does this information tellyou a. about the effect of sizeof preypopulationson the number of predators? If a largefood supply(prey)is available, then thepredator population can increase. b. about the effect of predators on the populations of their prey?

When the predator population becomes too large, they consume the food (prey) and so the overall

prey population is reduced. 8. What other factor would influencethe sizeof the hare population in addition to the sizeof the

population of lynx? The amount offood available to the hares.

STOP

180

POGIV' Activities for High School

Model 2 --Symbiosis

Organism 1 Organism 2

Dog

Flea

Fungus

Algae

Termite

Cellulosedigesting bacteria

Description of the relationship

Symbio tic Relationship

The fleafeeds on blood from the dog. There Parasitism is no benefit to the dog and che itching and bites may lead to infection.

The photosynthetic algaeprovide food for Mutualism the fungus, which in turn provides a suitable living environment for the algae.

The bacteria in the gut of the termite breakdown and feed on some of the cellulosetaken in by the termite.The termite would be unable to digest cellulose without these bacteria and they gain an additional source of nutrition from the surplus digested cellulose.

Mutualism

Shark

Remora

The Remora fish swim alongside the shark and cakescraps of food that the shark drops during feeding. The shark does not eat che Remora and appears unaffected by its presence.

Commensalism

Caccle

Cattle egret

The cattle egret follows herds of cattle and eats the insects that the cattle stir up as they move through the grassland.The cattle appear to be unaffected by the egrets.

Commensalism

Human

Tapeworm

The tapeworm lives in che small intestines where it feeds and grows, robbing the human of essential nutrients.

Pa rasitism

9. Refer co the information given in Model 2. a. In the dog and flea relationship,is there a benefit for one of the organismsor for both? Only one--theflea. b. Is either the dog or the flea harmed by chis relationship? The dog is harmed. c. Which other relationshipin Model 2 is similar to chatbetween the dog and flea? Human and tapeworm.

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10. Refer to the fungus and algaerelationshipin Model 2. a. Is there a benefit for one of the organismsor for both?

Both.

b. Is either the fungus or the algae harmed by this relationship?

No.

c. Which ocher relationship in Model 2 is similar co that between the fungus and the algae? Termite and cellulose-digestingbacteria.

I l. Refer co the shark and remora relationship in Model 2. a. In che shark and remora relationship, is there a benefit for one of the organisms or for both? Only one benefits, the remora. b. Is either the shark or the remora harmed by chis relationship?

c. Which other relationship in Model 2 is similar co that between the shark and che remora? Cattle and cattle egret.

Read This!

Symbiotic relationships are identified by how they affect the organisms involved. The three types of symbiotic relationships are listed below.

Mutualism: Both organisms benefit from the relationship. ? Parasitism: One organism benefitsand the ocheris harmed. ? Commensalism: One organism benefitsand there is no effect on cheother.

12. Using the information from che Read This!box, label each of the relationships in Model 2 as mutualism, parasitismor commensalism. SeeModel 2.

13. With your group, choose one of the organism pairs from Model 2 and justify why you categorized the relationship as you did. Answers will vary. Students sh01ddexplain how the description meets the definition of the symbiotic relationship.

STOP

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POGIIP' Activities for High School Biology

Model 3 --Inter- and Intra-specific Competition

Graph A

Graph B

P. aurelia and P. caudatum grown separately

P. aurelia and P. caudatum grown together

o

P. aurelia

Oc:

3

P. coudatum

O

P. aurelia

P. coudatum

20 Number of Days

20 Number of Days

Graph C

Rate of growth of R. tigrina tadpoles in populations of different sizes.

1.0

0.8

A--Minimum mass needed

for metamorphosis

0.6

to occur.

0.4 0.2

01 2345678 9 10 Time (weeks)

5 individuals

40 individuals 60 individuals -- -- --

160 individuals

14. What are the names of chespecies in graphs A and B in Model 3? P. aurelia and P. caudatum.

15. Which graph shows competition between two different species?

16. Which graph in Model 3 shows population growth for only one species?

17. What is the difference between the growing conditions in graph A and graph B? In graph A the two speciesare grown separatelyand in graph B they are grown together.

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